1. Field of the Invention
The present invention relates to a guided vehicle, specifically to a guided vehicle equipped with rubber tires suspended by means of air springs used as secondary suspensions or a magnetic levitated vehicle, etc.
2. Description of the Related Art
Recent years, a medium capacity transit system, one of so-called new transit systems, in which guided vehicles equipped with rubber tires travel along exclusive guideways, has become widespread, and also development work toward practical use of magnetically-levitated trains is making advances. Full automatic operation of unmanned vehicles is performed in many of these transit systems. In some case the vehicle has guide wheels to guide it along the sidewall of the guideway.
Many of vehicles used in these new transit system or magnetic levitation system adopt pneumatic suspension as secondary suspensions for the sake of improving ride quality as shown in FIG. 7. In FIG. 7, reference numeral 100 is a body of a vehicle, 102 are air springs, 104 are tires, and 106 are guide wheels for guiding the vehicle along a guide rail not shown in the drawing. Left and right tires 104 are connected by an axle covered by an axle housing.
However, the air spring 102 must be located between the axle housing and the vehicle body 100, so each of the left and right air springs 102 is located at a position inner side from the left and right tires 104 respectively when tires 104 are used. The air spring 102 is composed of a bellows (or diaphragm) made of multi-plied rubber and reinforcing fiber layers and it can withstand a pressure of about 2.0 MPa, however, operating pressure is limited generally to 0.59 MPa or lower in consideration of durability of the bellows (or diaphragm).
Further, the bellows (or diaphragm) act as a spring by its expansion and contraction in vertical directions, so it is shaped to be circular in plan view in order to evade occurrence of local stress concentration which tends to occur if it is not circular in plan view. Therefore, when load to be supported by the air spring increases; the outer diameter of the air spring must be increased to increase its effective load area so that inside pressure of the bellows (or diaphragm) does no exceed the limit pressure. With air springs of large outer diameter, distance between the left and right air springs decreases, resulting in decreased rolling stiffness of the vehicle, that is, resistance to rolling of the vehicle decreases and ride quality is deteriorated. Further, in order to manufacture an air spring of large outer diameter unpracticed heretofore, it is needed to make a mold to form constituent parts, which requires fairly large cost.
Furthermore, with decreased distance between the left and right air springs, tilt adjustment of the vehicle body by adjusting the left and right air spring becomes not easy, and more time is needed to perform tilt adjustment of the vehicle body. It may be thinkable to broaden the tread, i.e. distance between the left and right wheel in order to locate the air springs of increased outer diameter increased to comply with increased vehicle load without decreasing center distance of left and right air spring. However, larger cross-section surface of guideways are required with increased tread of the guided vehicle, a lot of money will be required for provision of infrastructure. As to domestic new transit systems, vehicle width is determined in standardization and cannot be increased by preference.
As to an art to improve stiffness and damping of rolling of a vehicle equipped with air springs, a rear suspension device of a bus is disclosed for example in a patent literature 1 (Japanese Laid-Open Patent Application No. 2001-47830).
According to the literature, in a rear suspension device comprising; air springs located just under the straight side members (component members of the chassis frame) at positions front ward and rear ward from the rear axle housing, and shock absorbers located between the rear axle housing and the straight side members to attenuate vibration of the bellows (or diaphragm) of the air springs; the rear shock absorbers are located outer side from the side members, thereby increasing distance between the left and right shock absorbers, and thereby making the distance between the left and right shock absorber of the rear shock absorbers nearly equal to that of the front shock absorbers. By this, stiffness of rolling and damping of the rolling effectuated by the rear shock absorber is improved, and the effects of suppression of rolling by the rear and front shock absorber become nearly balanced.
In a patent literature 2 (Japanese Laid-Open Patent Application No. 2005-96724) is disclosed a method of controlling tilting of a vehicle body. The invention relates to tilt controlling of the body of a vehicle having front and rear bogies on which the vehicle body is supported by means of air springs.
Tilt control is performed by controlling supply and drain of air to four air springs located on the front and rear bogies at left and right positions respectively. According to the invention, when the vehicle runs through a curve section of rail road, two air springs of either of the front or rear bogie are communicated with each other so that the vehicle body is supported by apparent three-point support on the bogies. In this state, tilting of the vehicle body is controlled by supplying or draining air only to or from air springs not communicated with each other. In this way, air consumption for body tilt control can be decreased.
However, the rear suspension device of a bus as disclosed in the patent literature 1 aims to attain low-floor construction of a bus. As rear axle load is two times that of the front axle in the bus, two air springs of the same size are attached at a forward and rearward position from the rear axle housing for each of left and right side of the vehicle. The left and right air springs depart from each other by more than a little distance, and the two air springs are not communicated with each other. Therefore, the rear axle is supported by four separate air springs, and when there is a bias or deviance in distribution of sprung weight among the four rear air springs, height and tilt adjustment of the vehicle by controlling each separate air spring becomes difficult. That is not problematic in the case of trucks and buses, however, in the case of guided vehicles, it is necessary to severely control difference between the platform surface and floor surface of the vehicle to be in a range of ±few millimeters, so that becomes problematic.
The method and device of controlling tilting of the vehicle body aims only to decrease consumption of air required to tilt the vehicle body when the vehicle runs through a curve section of the rail road by communicating the left and right air spring of either of the front or rear bogie, and can not resolve such a problem that occurs when air springs of increased outer diameter are used in order to comply with increased axle load, i.e. decrease in rolling stiffness due to decreased distance between the left and right air spring.